1. Field of the Invention
This invention relates to a security device for a slide fastener and relates particularly, though not exclusively, to a security device for re-useable security envelopes.
2. Background Art
Re-useable security envelopes are commonplace for the transportation of documents or articles between various offices of a business or government departments. The envelope is made from a sturdy material, e.g., plastics, canvas, et cetera, which is sealed around the edges. A slide fastener or zipper closes an opening in the envelope to allow entry to the envelope. Articles are placed in the envelope and the zip slider is drawn across the zip chain of teeth fitted to the tapes of the slide fastener to close the envelope. In order to prevent tampering of the contents of the envelope a security device is fitted to both the zip chain and the security envelope to prevent, or make evident, any unauthorized access to the envelope. Typically, the security device is fitted to secure the slider and includes a disposable numbered identification tag which must be broken to release the slider. Any tampering is clearly visible if the tag has been broken. It is not possible to substitute a tag that has been broken to avoid suspicion that the security of the envelope has been compromised as each tag has its own unique number with a no repeat in six million numbered combinations.
Examples of such devices are shown in U.S. Pat. Nos. 4,112,990, 4,008,914, 4,602,405 and 3,955,842. These devices which have proved popular as the disposable tags or plugs that provide visual evidence of tampering, are inexpensive to mass produce and provide a certain degree of security. Unfortunately, these devices can be easily manipulated using dexterity and lock picks to release the disposable tag or plug without damage thereto. The slide fastener can then be released and the contents of the envelope taken or substituted. The tag or plug can then be re-inserted in the usual manner and there will be no evidence of tampering. The applicant has determined that the major problem is the external exposure of both the slider and the security device. This allows a thief ready access using lock picks and similar tools.
It is an object of the present invention to provide a security device for a slide fastener that provides enhanced security over the prior art.
A further object of the invention is to provide a security device for a slide fastener where the slider of the slide fastener is hidden when in use.
With these objects in view, the present invention in a preferred aspect may provide a security device for a slide fastener, the security device including a housing adapted to be fitted to an object to which the slide fastener is attached, the housing substantially surrounding the slider of the slide fastener in its fully closed position, a closure member adapted to co-operate with the housing which, in use, covers the slider to prevent access thereto and a frangible locking element adapted to link the housing to the closure member, the locking element being resiliently yieldable and slidably insertable into the closure member but not retractable therefrom without fracturing the frangible locking element.
Preferably the closure member is attached at one end to a puller and the puller is attached to the slider. In a preferred embodiment the closure member can pivot about the housing and block withdrawal of the slider from the housing in its closed position.
In a practical embodiment the housing includes a receptacle or guide member which aligns with a slot in the closure member in its closed position and the frangible locking element includes barbs or hooks which lock behind the guide member to prevent extraction of said frangible locking element from the housing and the closure member.
The housing may include a spreader which spreads the barbs apart during insertion of the frangible locking element into the closure member to further assist in preventing extraction of the frangible locking element from the housing and the closure member.